1. Field of the Invention
The present invention relates to a device and method for detecting explosives. More particularly, the present invention relates to an apparatus and method for generating and detecting Terahertz radiation to positively identify explosive devices carried on human or animal subjects.
2. Description of Related Art
The purpose of this invention is to address privacy concerns that plague the millimeter waver/Terahertz imagers that are being installed in various U.S. and international airports. The current full body imagers can detect explosives using millimeter and Terahertz waves directed against clothing or packing material. However, privacy concerns persist due to the inevitable picturing and highlighting of human body parts.
It is well known that organic molecules have unique vibrational and rotational frequencies and that the rotational frequencies lie in the Terahertz regime. The Terahertz waves also have the capability to excite these rotational frequencies within the molecules of explosive materials. The commonly used explosive RDX, for example, has spectral lines at 0.82, 1.05, 1.50, 1.96, 2.20, 3.08 and 6.73 THz. A simultaneous detection of these rotational frequencies or wavelengths, through several layers of clothing, will constitute a very robust detection of RDX. Other explosives can be similarly detected. In addition to spectral specificity, good imaging resolution is inherently possible as the wavelengths associated with Terahertz, 15 μm to 1 mm, are short. However, privacy concerns still exist in this kind of imaging hence imaging will not be attempted.
The role Terahertz frequencies can play in the detection of explosives has been well known for some time. However, it has been difficult to make robust THz sources or detectors. Terahertz frequencies (0.5 to 5.0 THz) occupy the region of electromagnetic spectrum that is sandwiched between microwaves and infrared, and these frequencies are too high to be produced by conventional electronics and too low to be produced by solid state lasers. The conventional sources of THz are ultra-fast laser switches, pumped gas lasers, optical difference generation techniques, frequency doubling diodes and quantum cascade lasers. All of these require cumbersome equipment and large power sources.
Other detection systems like the Ion Mobility Spectrometer require a small sample of the explosive to be physically brought to the machine for analysis. In the end, none of the prior art discloses an effective and efficient way to detect explosives. Therefore, a need exists to develop a novel alternative that can detect and positively identify explosives in real time without the drawbacks evident in the prior art.